25 



Further afield, Mount Erebus rises as a full-bodied cone with its base 12 miles and its summit 20 miles 

 distant. The rocks found at its base have a specific gravity of approximately 2-9. The mountain lies 

 north by east of Winter Quarters, and is 12,000 feet high. 



Mount Terror, lying 40 miles east of the ship, is only 10,000 feet high, ;iiid is romped of Uwic rocks 

 of specific gravity 2 "9, with small local intrusions of trachyte of a specific gravity of 2 '4. The two art: 

 joined by a ridge some 8000 feet high and of similar rock to that which forms the masses of Erebus and 

 Terror. 



There is no important land development to the southward, there being only two islands under .'iOOO fi-rt 

 high and composed chiefly of basalt of specific gravity about 2-9. These are respectively 15 and 20 miles 

 distant from the ship. 



Mount Discovery lies south-west from the ship at a distance of 30 miles. It is also conical, with a 

 height of 8000 feet and the diameter of the base some 10 miles. It appears to lie chiefly composed of the 

 basic rock so common in this locality. 



Turning to the west there is a totally different development. A great mountain chain running nearlv 

 due north and south lies at a distance of 40 miles from the ship and rises to heights of 12,000 and 

 13,000 feet, and is on an average 11,000 feet high. This chain is composed of granites, diabases, and 

 quartzites. The granites form the core of the chain and rise to a height of 4500 feet above sea-level. 

 They vary in composition and have a specific gravity between 2 6 and 2 7. 



Above this occurs a diabase up to a height of 8000 feet. This rock lies practically horizontally on the 

 plutonic rocks (though interrupted by faults) and has a specific gravity of roughly 2 -8, while above it and 

 also horizontal a sandstone occurs which has a specific gravity not greater than 2 '67. This practically 

 completes the series of the Prince Albert Mountains. 



Near Hut Point the soundings showed McMurdo Sound to be comparatively shallow. The water 

 quickly deepened from 2 fathoms at Hut Point to 180 fathoms a mile further out in the Sound to the 

 west, while 10 miles away to the west-north-west the sounding was 100 fathoms. The deepest sounding 

 was 400 fathoms at a point 2 miles south-east of Observation Hill, and other soundings showed that the 

 water was much deeper to the south and the south-east than to the north and north-west of Winter Quarters. 

 The Sound therefore may be taken to be 25 miles wide with an average depth of 200 fathoms. The 

 ship anchored in Winter Harbour had 9 to 11 fathoms of water, while on the north side of Hut Point the 

 water quickly deepened to 50 fathoms close in to the land. Hut Point itself .is continued half a mile to 

 the south-west below water in a shoal which gives soundings of from 2 to 25 and 40 fathoms. 



Most of the above geological information has been kindly supplied by Mr. H. T. FERRAR, Geologist to 

 the Expedition. It may be possible from this geological information to investigate the effect of topo- 

 graphical irregularities and determine a correction for the density of the local rocks. 



CONCLUDING KEMARKS. 



In the following reductions the period has been determined for each separate set of 50 coincidences, and 

 corrected independently for temperature, pressure, &c. In the reduction of the pressure observations the 

 temperature of the mercury in the barometer has been assumed to be the same as that of the mercury in 

 the U-tube, since they were quite close to one another. The difference in the height of the columns was 

 then corrected for temperature. 



It must be borne in mind that the observations of July, August, and September were taken in what is 

 practically the middle of the Antarctic winter, or, more correctly, during the coldest months of the year. 

 The February observations are at the end of the comparatively warm summer, when the pack ice has 

 moved far to the north, and after huge masses of ice have been shed from the glaciers and the great ice 

 fields of the Antarctic lands, and in turn drifted away to the north. 



My thanks are due to Engineer Commander E. W. SKELTON, E.N., who not only rendered most 

 valuable services in assisting to set up the pendulum apparatus, ifcc., but soon made himself thoroughly 

 competent in taking observations. Independent sets of swings were taken by him on every occasion at, 

 Winter Harbour. 



K 



